2.1 Field of the Invention
The present invention relates to compounds that have biological activity with respect to estrogen receptors and to the use of such compounds to treat diseases and disorders related to estrogen receptor activity. More particularly, the present invention provides selective estrogen receptor modulators ("SERMs"). The present invention therefore relates to the fields of medicine, medicinal chemistry, biochemistry, and endocrinology.
2.2 Background
Estrogen is a hormone critical to normal human development and function. Although estrogen is the predominant "sex hormone" in women, in whom estrogen controls the development of female sex characteristics and the development and function of the reproductive system (Berkow, Beers et al 1997), it is also found in men (Gustafsson 1998). Women produce estrogen primarily in the ovaries; however, estrogen affects a variety of physiological functions in women including body temperature regulation, maintenance of the vaginal lining, and preservation of bone density (Jordan 1998). In addition, estrogen provides additional effects that are related to its ability to modulate production of cholesterol in the liver, as demonstrated by the reduced occurrence of atherocsclerosis in women compared to men due in part to the reduction of low-density lipoprotein ("LDL") (Jordan 1998). Estrogen has also been implicated in delaying and/or reducing the severity of Alzheimer's Disease (Jordan 1998).
Failure to produce estrogen has profound physiological consequences in females. Failure to produce estrogen resulting from incomplete or absent ovary development (Turner's Syndrome) causes deficiencies in the skin, bone (e.g., severe osteoporosis), and other organs severely affecting the life of the afflicted individual (Dodge 1995). In normal women, estrogen production falls sharply upon the onset of menopause, usually at about 50 years of age. The effects of the loss of estrogen production include increased atherosclerotic deposits (leading to greatly increase incidence of heart disease), decreased bone density (osteoporosis), and fluctuations in body temperature among others (Jordan 1998). Often, the effects of reduced estrogen production are addressed by hormone replacement therapy (Dodge 1995; Berkow, Beers et al. 1997; Jordan 1998).
However, estrogen also has undesirable effects. In menopausal women, supplementation of estrogen is associated with alleviation of the above-described unwanted effects. But, administration of estrogen is also associated with increased risks for breast and endometrial cancer as well as blood clots (Jordan 1998). The increased risk of endometrial cancer can be addressed by the administration of progesterone (or its synthetic analog progestin) to reinitiate menstruation and thereby shed potentially malignant cells, but many older women find this undesirable (Jordan 1998). Breast cancer, however, is by far the greater risk of estrogen replacement therapy, affecting one woman in every 15 between the ages of 60 and 79 (Jordan 1998).
Thus, for a long time the treatment options for the serious health problems caused by a failure to produce estrogen were limited and entailed severe risks. However, the discovery that some agents acted as estrogen agonists in some tissues (e.g., bone) and as an antagonists in other tissues (e.g., breast) provided hope that more effective treatments for estrogen loss could be found (Gradishar and Jordan 1997; Gustafsson 1998; Jordan 1998; MacGregor and Jordan 1998). The best known of these so-called Selective Estrogen Receptor Modulators ("SERMs"), tamoxifen, has been demonstrated to have therapeutic utility in treating and preventing breast cancer and lowering LDL concentrations; yet, without significant reduction bone density (Jordan 1998; MacGregor and Jordan 1998). However, tamoxifen has been associated with endometrial cancer and venous blood clots (Jordan 1998; MacGregor and Jordan 1998). In addition, tumor resistance to tamoxifen can occur (MacGregor and Jordan 1998).
Tamoxifen has been followed recently by newer SERMs, in particular raloxifene, that promise to provide many of tamoxifen's benefits with fewer risks (Howell, Downey et al. 1996; Gradishar and Jordan 1997; Gustafsson 1998; Jordan 1998; Purdie 1999; Sato, Grese et al. 1999). These newer SERMs, including idoxifene (Nuttall, Bradbeer et al. 1998), CP-336,156 (Ke, Paralkar et al. 1998), GW5638 (Willson, Norris et al. 1997), LY353581 (Sato, Turner et al. 1998) are part of the second- and third generation of partial estrogen agonists/antagonists. In addition, a new generation of pure antiestrogens such as RU 58,688 (Van de Velde, Nique et al. 1994) have been reported. A large number of additional partial and pure estrogen agonist/antagonist compounds and treatment modalities have reported recently (Bryant and Dodge 1995; Bryant and Dodge 1995; Cullinan 1995; Dodge 1995; Grese 1995; Labrie and Merand 1995; Labrie and Merand 1995; Thompson 1995; Audia and Neubauer 1996; Black, Bryant et al. 1996; Thompson 1996; Cullinan 1997; Wilson 1997; Miller, Collini et al. 1999; Palkowitz 1999; Wilson 1999).
However, no one drug candidate has emerged to fill the needs of women who require the benefits of estrogen replacement to live productive lives and/or treatments for estrogen-dependent cancers. The efforts to develop better partial and pure estrogen agonists and antagonists has been aided by several recent developments, including the discovery that human estrogen receptor has at least two isoforms ("ER.alpha." and "ER.beta.") and the crystal structure of ER.alpha. that have permitted high-resolution structure-acitivty relationship studies (Sadler, Cho et al. 1998). Recently, a study of the application of combinatorial synthetic methods combined with three-dimensional structure-activity analysis to develop SERMs having optimal therapeutic profiles was reported (Fink, Mortensen et al. 1999). That study examined several heterocyclic motifs (imidazoles, thiazoles, pyrazoles, oxazoles, and isoxazoles) and identified certain pyrazole motifs as being well suited for combinatorial development of SERMs. The relative binding effectiveness of the pyrazoles viz. the other motifs was based on its ability to carry four substituents in addition to polarity consideration (see p. 215). In particular, the study referred the capacity of the pyrazole motif to carry four substituents explained the binding effectiveness pyrazoles compared to the poor binding results found for the oxazole, thiazole, and isoxazole motifs.
However, despite these recent advances no drug candidate has emerged to fill the needs of women who require the benefits of estrogen replacement to live productive lives and/or treatments for estrogen-dependent cancers. The present invention addresses these and other needs.